A fiber optic sensing system comprises a housing disposed in a flow path, and a fiber optic sensor. The fiber optic sensor comprises an optical fiber secured in the housing, a Bragg grating, a light source for transmitting light to the optical fiber, and a detector for detecting light filtered by the Bragg grating of the optical fiber and monitoring wavelength changes of the detected light. The fiber is substantially perpendicular to the flow path. The housing defines an opening at an upstream side to allow flow through the flow path to exert a pressure on the optical fiber and cause a deformation of the Bragg grating.